Getting Started with MySQL I

What is Database?
• A database is a structured collection of data. Here are some
typical examples of databases:
• An online store database that stores product details, customer
details and orders
• A database for a web forum that stores members, forums, topics
and posts
• A database for a blog system, such as WordPress, that stores
users, blog posts, categories, tags, and comments
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What is Relational Database Management
System?
A Relational DataBase Management System (RDBMS) is a software that:
• Enables you to implement a database with tables, columns and indexes.
• Guarantees the Referential Integrity between rows of various tables.
• Updates the indexes automatically.
• Interprets an SQL query and extracts information from various tables
based on SQL query
We use Relational Database Management Systems (RDBMS) to store and
manage huge volume of data. This is called relational database because all
the data is stored into different tables and relations are established using
primary keys or other keys known as foreign keys.
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RDBMS Terminology
4
Database is a collection of tables, with related data.
Table is a matrix with data. A table in a database looks like a simple spreadsheet.
Column
One column (data element) contains data of one and the same kind, for
example the column postcode.
Row
(= tuple, entry or record) is a group of related data, for example the data of
one subscription.
Redundancy Storing data twice, redundantly to make the system faster.
Primary Key
is unique. A key value can not occur twice in one table. With a given key,
you can find at most one row.
Foreign Key
is the linking pin between two tables.
Compound
Key
(composite key) is a key that consists of multiple columns, because one
column is not sufficiently unique.
Index in a database resembles an index at the back of a book.
Referential
Integrity
makes sure that a foreign key value always points to an existing row.

Introduction to MySQL
MySQL Database:
MySQL is a fast, easy-to-use RDBMS being used for many small and big businesses.
MySQL is developed, marketed, and supported by MySQL AB, which is a Swedish
company.
Key Advantages over other Databases:
• MySQL is released under an open-source license. So you have nothing to pay to use
it.
• MySQL is a very powerful program in its own right. It handles a large subset of the
functionality of the most expensive and powerful database packages.
• MySQL uses a standard form of the well-known SQL data language.
• MySQL works on many operating systems and with many languages including PHP,
PERL, C, C++, JAVA, R etc.
• MySQL data can be called in R for data analysis
5

How to Install MySQL
• Download the files from below link for installation of MySQL.
https://dev.mysql.com/downloads/mysql/
Use the appropriate archive file for download 32-bit or 64-bit.
• For Excel connection go to below link-
https://dev.mysql.com/downloads/windows/
− Click on "MySQL for Excel“
− Copy both the installation file in one folder then start the installer community
Run both the setups in their respective order
Use MySQL Workbench for working with MySQL. It gets downloaded and installed
during the above process.
MySQL Workbench is a visual database design tool that integrates SQL
development, administration, database design, creation and maintenance into a
single integrated development environment for the MySQL database system.
7

MySQL Workbench
8
SQL query panel
Output (results)
from statements
Log of executed
statements
Executes the SQL statement
Or
Press ‘ctrl + Enter’ to execute
the statements

Creation of Database Overview
In MySQL, a database is a collection of objects that are used to store and
manipulate data such as tables, database views, triggers, stored procedures, etc.
Syntax:
CREATE DATABASE [IF NOT EXISTS] database_name;
Displaying a Database
Syntax:
SHOW DATABASES;
Selecting a database to work with
Syntax:
USE database_name;
Removing Databases
Syntax:
DROP DATABASE [IF EXISTS] database_name;
The IF NOT EXISTS is an optional clause of the statement. The IF NOT EXISTS
clause prevents you from an error of creating a new database that already exists in
the database server. You cannot have 2 databases with the same name in a MySQL
database server.
* 9

Creation of Database Overview
‘Student’ database created
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CREATE DATABASE student;
SHOW DATABASES;
Drop database student;
SHOW DATABASES;
‘Student’ database dropped

SQL Statements – DDL and DML
DDL is short name of Data Definition Language. These statements are used to define
and modify a database or table structure and schema.
DML is short name of Data Manipulation Language. These statements affect records
in a table. These are used to perform basic operations on data such as selecting a few
records from a table, inserting new records, deleting unnecessary records and
updating/modifying existing records.
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SQL Statements
DDL:
CREATE
ALTER
DROP
DML:
SELECT
INSERT
UPDATE
DELETE

DDL Statements - CREATE
Create tables (note that database is made up of tables which are like
data frames in R)
The table creation command requires:
• Name of the table
• Names of fields
• Definitions for each field
Syntax:
Here is generic SQL syntax to create a MySQL table:
CREATE TABLE table_name (column_name column_type);
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DDL Statements - CREATE
Create tutorials_tbl in student database.
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Use student
Create table tutorials_tbl(
tutorial_id INT NOT NULL AUTO_INCREMENT,
tutorial_title VARCHAR(100) NOT NULL,
tutorial_author VARCHAR(40) NOT NULL,
submission_date DATE,
PRIMARY KEY ( tutorial_id ) );
select * from tutorials_tbl;
INT, VARCHAR, DATE are data
types
This command returns all the
fields of table

DDL Statements - ALTER
Alter tables:
The ALTER TABLE statement allows you to add a column, drop a column,
change the data type of column, add primary key, rename table, and many
more.
Syntax:
ALTER TABLE table_name action1[,action2,…]
Using MySQL ALTER TABLE statement to add a new column into a table
ALTER TABLE table_name
ADD COLUMN column_name DECIMAL(2,1) NULL
AFTER column_name;
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Add a new column to tutorials_tbl
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ALTER TABLE tutorials_tbl
ADD COLUMN tutorial_fee DECIMAL(2,1) NULL
AFTER tutorial_author;

Using MySQL ALTER TABLE to drop a column from a table.
DROP COLUMN column_name;
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ALTER TABLE tutorials_tbl
DROP COLUMN tutorial_fee;
Renaming table using MySQL ALTER TABLE statement
RENAME TO new_table_name;

DDL Statements - DROP
It is very easy to drop an existing MySQL table, but you need to be
very careful while deleting any existing table because data lost will
not be recovered after deleting a table.
Syntax:
Here is generic SQL syntax to drop a MySQL table:
DROP TABLE table_name;
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DDL Statements - DROP
Delete tutorials_tbl table
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DROP TABLE tutorials_tbl;

DML Statements - INSERT
To insert data into MySQL table, you would need to use SQL INSERT INTO
command. You can insert data into MySQL table by using mysql> prompt or
by using any script like PHP.
Syntax:
Here is generic SQL syntax of INSERT INTO command to insert data into
MySQL table:
INSERT INTO table_name ( field1, field2,...fieldN )
VALUES ( value1, value2,...valueN );
To insert string data types, it is required to keep all the values in double or
single quote, for example:- "value".
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DML Statements - INSERT
Insert 3 records into tutorials_tbl.
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INSERT INTO tutorials_tbl (tutorial_title, tutorial_author,
submission_date)
VALUES ("Learn PHP", "John Poul", NOW());
submission_date)
VALUES ("Learn MySQL", "Abdul S", NOW());
submission_date)
VALUES ("JAVA Tutorial", "Sanjay", '2007-05-06');
Here, we have not provided tutorial_id because at the time of table creation, we had
given AUTO_INCREMENT option for this field. So MySQL takes care of inserting these IDs
automatically.
NOW() is a MySQL function, which returns current date and time.

DML Statements – INSERT and UPDATE
Insert or Update in MySQL using ON DUPLICATE KEY UPDATE
INSERT ON DUPLICATE KEY UPDATE is a MySQL extension to the INSERT
statement. If you specify the ON DUPLICATE KEY UPDATE option in the
INSERT statement,the new row causes a duplicate value in the UNIQUE or
PRIMARY KEY index and MySQL performs an UPDATE to the old row based
on the new values.
Syntax:
INSERT INTO table(column_list)
VALUES(value_list)
ON DUPLICATE KEY UPDATE column_1 = new_value_1, column_2 =
new_value_2, …;
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DML Statements – UPDATE
We use the UPDATE statement to update existing data in a table.
We can use the UPDATE statement to change column values of a single row,
a group of rows, or all rows in a table.
Syntax:
UPDATE table_name
SET
column_name1 = expr1,
column_name2 = expr2,
...
WHERE
condition;
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DML Statements – UPDATE
23
update tutorials_tbl
set tutorial_author = 'Anand'
where tutorial_id = 1;

DML Statements – DELETE
MySQL DELETE statement allows you to remove records from not only one
table but also multiple tables using a single DELETE statement.
Syntax:
DELETE FROM table
[WHERE conditions]
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Delete from tutorials_tbl
where tutorial_id = 3;

DML Statements – SELECT
The SQL SELECT command is used to fetch data from MySQL database. You
can use this command at mysql> prompt as well as in any script like PHP.
Syntax:
Here is generic SQL syntax of SELECT command to fetch data from MySQL
table:
SELECT field1, field2,...fieldN
FROM table_name1, table_name2...
[WHERE Clause] [OFFSET M ][LIMIT N]
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You can use one or more tables separated by comma to include various
conditions using a WHERE clause, but WHERE clause is an optional part of
SELECT command.
You can fetch one or more fields in a single SELECT command.
You can specify:
• star (*) in place of fields. In this case, SELECT will return all the fields.
Eg. SELECT * from tutorials_tbl ;
• any condition using WHERE clause.
• an offset using OFFSET from where SELECT will start returning records. By
default offset is zero.
• use LIMIT attribute to limit the number of returns 26

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use world;
select code, name, continent, region, population
from country;

DML Statements – SELECT with WHERE
clause
28
use world;
select code, name, continent, region, population from country
where continent = 'Asia';

DML Statements – SELECT with ORDER BY
clause
29
The ORDER BY clause allows you to:
• Sort a result set by a single column or multiple columns.
• Sort a result set by different columns in ascending or descending order.
Syntax:
SELECT column1, column2,...
FROM tbl
ORDER BY column1 [ASC|DESC], column2 [ASC|DESC],...

clause
30
use world;
from country
order by name asc;

clause
31
use world;
from country
order by name desc;

DML Statements – SELECT with DISTINCT
and WHERE clause
32
In order to remove duplicate rows, you use the DISTINCT clause in the Select
Statement
Syntax:
SELECT DISTINCT columns
FROM table_name;
The WHERE clause allows you to specify exact rows to select based on a
particular filtering expression or condition.
Syntax:
SELECT columns
FROM table_name
WHERE
where_conditions;

DML Statements – SELECT with DISTINCT
and WHERE clause
33
use world;
select distinct continent from country where
population>100000;

DML Statements – SELECT with UNION
operator
34
MySQL UNION operator allows you to combine two or more result sets from
multiple tables into a single result set.
Syntax:
SELECT column1, column2
UNION [DISTINCT | ALL]
SELECT column1, column2
UNION [DISTINCT | ALL]
There are some rules that you need to follow in order to use the UNION operator:
• The number of columns appears in the corresponding SELECT statements
must be equal.
• The columns appear in the corresponding positions of each SELECT
statement must have the same data type or, at least, convertible data type.

DML Statements – SELECT with alias (for
columns)
35
MySQL supports two kinds of aliases which are known as column alias and table
alias.
MySQL alias for columns
Sometimes the column names are so technical which makes the query’s output
very difficult to understand. To give a column a descriptive name, you use a
column alias.
Syntax:
SELECT
[column_1 | expression] AS descriptive_name
FROM table_name;
If the alias contains space, you must quote it as the following:
SELECT
[column_1 | expression] AS `descriptive name`
FROM table_name;

columns)
36
use employees;
SELECT
CONCAT_WS(', ', “lastName”, “firstname”)
FROM employees;
SELECT
CONCAT_WS(', ', “lastName”, “firstname”) AS `Full name`
FROM employees;
CONCAT_WS function is used to concatenate first name and last name.
Using Alias we can make the column heading more readable.

columns)
37

tables)
38
MySQL alias for tables
You assign a table an alias by using the AS keyword as the following syntax:
table_name AS table_alias
You often use the table alias in the statement that contains INNER JOIN, LEFT
JOIN, self join clauses, and in subqueries.

INNER JOIN
39
Inner Joins
The MySQL INNER JOIN clause matches rows in one table with rows in other tables and
allows you to query rows that contain columns from both tables.
Before using MySQL INNER JOIN clause, you have to specify the following criteria:
• First, you have to specify the main table that appears in the FROM clause.
• Second, you need to specify the table that you want to join with the main table,
which appears in the INNER JOIN clause. Theoretically, you can join a table with
many tables. However, for better query performance, you should limit the number
of tables to join.
• Third, you need to specify the join condition or join predicate. The join condition
appears after the keyword ON of the INNER JOIN clause. The join condition is the
rule for matching rows between the main table and the other tables.

INNER JOIN
40
Syntax:
SELECT column_list
FROM t1
INNER JOIN t2 ON join_condition1
INNER JOIN t3 ON join_condition2
...
WHERE where_conditions;
For each row in the T1 table, the MySQL INNER JOIN clause compares it with
each row of the T2 table to check if both of them satisfy the join condition. When
the join condition is matched, it will return the row that combine columns in both
T1 and T2 tables.
Notice that the rows in both T1 and T2 tables have to be matched based on the join
condition. If no match found, the query will return an empty result set. This logic is also
applied if we join more than 2 tables.

INNER JOIN
41
The following Venn diagram illustrates how the MySQL INNER JOIN clause
works. The rows in the result set must appear in both tables: T1 and T2.

LEFT JOIN
42
The MySQL LEFT JOIN clause allows you to query data from two or more
database tables. The LEFT JOIN clause is an optional part of the Select
Statement, which appears after the FROM clause.
Syntax:
SELECT
T1.c1, T1.c2, T2.c1, T2.c2
FROM
T1
LEFT JOIN
T2 ON T1.c1 = T2.c1;

LEFT JOIN
43
LEFT JOIN clause allows you to select rows from the both left and right tables
that are matched, plus all rows from the left table ( T1 ) even there is no
match found for them in the right table ( T2 ).

LEFT JOIN
44
Example: In the example below, in database world though details for
Afghanistan do not exist in the city table, still that row is displayed in output
due to the Left Join keyword. In INNER JOINS this row would not have
appeared.

DML Statements – SELECT with GROUP
BY clause
46
The GROUP BY clause, which is an optional part of the SELECT statement,
groups a set of rows into a set of summary rows by values of columns or
expressions.
The GROUP BY clause returns one row for each group. In other words, it
reduces the number of rows in the result set.
Syntax:
SELECT
c1, c2,..., cn, aggregate_function(ci)
FROM
table
WHERE
where_conditions
GROUP BY c1 , c2,...,cn;

BY clause
47
use world;
Execute the highlighted Select command to see the impact of aggregate
function

BY and HAVING clause
48
The MySQL HAVING clause is often used with the GROUP BY clause. When
using with the GROUP BY clause, we can apply a filter condition to the
columns that appear in the GROUP BY clause. If the GROUP BY clause is
omitted, the HAVING clause behaves like the WHERE clause.
Eg.
SELECT
ordernumber,
SUM(quantityOrdered) AS itemsCount,
SUM(priceeach) AS total
FROM
orderdetails
GROUP BY ordernumber
HAVING total > 1000;

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Execute the below SELECT command in world database.

50
Execute the below SELECT command in world database.

DML Statements – Subquery
51
A MySQL subquery is a query that is nested inside another query such as SELECT,
INSERT, UPDATE or DELETE. In addition, a MySQL subquery can be nested inside
another subquery.
A MySQL subquery is also called an inner query while the query that contains the
subquery is called an outer query.
MySQL subquery with IN and NOT IN operators
If a subquery returns more than one value, you can use other operators such as IN or
NOT IN operator in the WHERE clause.
MySQL subquery with EXISTS and NOT EXISTS
When a subquery is used with EXISTS or NOT EXISTS operator, a subquery returns a
Boolean value of TRUE or FALSE. The subquery acts as an existence check.

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SELECT customerNumber,checkNumber,amount
FROM payments
WHERE amount = (
SELECT MAX(amount)
FROM payments
);
SELECT customerName
FROM customers
WHERE EXISTS (
SELECT priceEach * quantityOrdered
FROM orderdetails
WHERE priceEach * quantityOrdered > 10000
GROUP BY orderNumber
);

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MySQL subquery in FROM clause:
When you use a subquery in the FROM clause, the result set returned from a
subquery is used as a table. This table is referred to as a derived table or
materialized subquery.
SELECT max(items),
min(items),
floor(avg(items))
FROM
(SELECT orderNumber,
count(orderNumber) AS items
FROM orderdetails
GROUP BY orderNumber) AS lineitems;

Getting Started with MySQL I

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